Effect of Er,Cr (YSGG Laser Root Conditioning on the Success of Root Coverage with Subepithelial Connective Tissue Graft): A Randomized Clinical Trial with a 6-Month Follow-Up.

Objectives
Finding predictable approaches for root surface biomodification is an important challenge in the treatment of gingival recession. This study sought to assess the root coverage percentage by subepithelial connective tissue graft (SCTG) following root surface conditioning with erbium, chromium: yttrium scandium gallium garnet (Er,Cr:YSGG) laser.


Materials and Methods
In this split-mouth, randomized clinical trial, 30 teeth with Miller's Class I and II gingival recession were treated with SCTG (the Langer and Langer technique) with (case group) or without (control group) root surface conditioning with Er,Cr:YSGG laser (wavelength=2780 nm, power=0.75 W, H mode, repetition rate=20 Hz). Recession depth (RD), recession width (RW), clinical attachment level (CAL), and probing depth (PD) were assessed at the baseline (one week before surgery) and at 2 and 6 months postoperatively. The amount of root coverage was quantified in the two groups. Data were analyzed using Friedman test and Wilcoxon signed-rank test.


Results
No significant difference was noted between the case and control groups in any parameter (P>0.05). Significant improvement occurred in all the measured parameters in the two groups after surgery (P<0.05). The mean root coverage at the end of the study period was 87% and 80% in the case and control groups, respectively (P=0.244), and complete root coverage was achieved in 66% and 60% of the samples in the case and control groups, respectively.


Conclusions
Root surface conditioning by Er,Cr:YSGG laser improved the mean root coverage and the percentage of complete root coverage. However, these changes were not statistically significant.


INTRODUCTION
Gingival recession is an unfavorable clinical condition characterized by the migration of the gingival margin from the cementoenamel junction (CEJ) towards the apex [1]. It results in denuding of the root surface and subsequent tooth hypersensitivity, root caries, and esthetic problems [2][3][4]. A high percentage of adults suffer from gingival recession [5]. Inflammatory periodontal disease, shortage of keratinized tissue, mechanical trauma, orthodontic movement, buccal positioning of the root, bone dehiscence, and abnormal frenal attachment are among the causes of gingival recession [5]. The main goal of treatment is to cover the denuded root surface to decrease tooth hypersensitivity and improve esthetics. Different therapeutic approaches suggested for this condition include surgical and non-surgical treatment modalities. Surgical approaches include free gingival graft [6], subepithelial connective tissue graft (SCTG) [7], coronally advanced flap [8], laterally sliding flap [9], double papillae flap [10], guided tissue regeneration [11], and acellular dermal matrix allograft [12]. The success rate of these procedures depends on several factors such as the position of the tooth, the class of recession, surgeon's experience and expertise, the surgical technique, and postoperative care [6][7][8][9][10][11][12][13][14]. Of the aforementioned procedures, SCTG has shown a high success rate and optimal predictability [13][14][15]. Thus, SCTG is considered the gold standard for the assessment of novel approaches [16]. Several studies have evaluated the efficacy of root surface conditioning aiming to improve the treatment results. It has been reported that mechanical debridement preserves the smear layer on the root surface and thus, prevents cell reattachment to this surface, compromising the process of regeneration and repair [17]. Several strategies have been proposed to overcome this problem including the use of root surface conditioners such as citric acid [18], ethylenediaminetetraacetic acid (EDTA) [19], tetracycline hydrochloride [20], and hydrogen peroxide [21], enamel matrix proteins [22], platelet-rich plasma [23], and recombinant human growth factors [24]. A recent study showed that laser irradiation eliminates the smear layer and exerts bactericidal effects and can therefore improve the condition of root surface for connective tissue attachment [25]. In contrast to carbon dioxide (CO2) and neodymium-doped yttrium aluminum garnet 1. Positive medical history contraindicating dental interventions 2. Presence of coagulation problems 3. Intake of medications interfering with periodontal health or the healing process 4. Alcohol consumption, tobacco use, or cigarette smoking 5. Disability or not showing up for followup sessions Scaling, root planing, and crown polishing were performed for all patients four weeks prior to surgery. Oral hygiene instructions were also given to the patients. To ensure the absence of periapical lesions, a parallel periapical radiograph was taken from the respective teeth, and the teeth were then randomly divided into two groups of case and control.

Assessment of clinical parameters:
The following clinical parameters were measured at the buccal surface of the teeth one week prior to surgery and at 2 and 6 months postoperatively

Calibration of the examiner:
The intraclass correlation coefficient was calculated for the assessment of the reproducibility of measurements, which was found to be 0.99, and indicated an excellent intraobserver agreement.

Treatment protocol:
For all patients, 10% povidone-iodine (Iran Najo Pharmaceutical Hygienic & Cosmetic Co., Tehran, Iran) and 0.2% chlorhexidine (Iran Najo Pharmaceutical Hygienic & Cosmetic Co., Tehran, Iran) were used for extraoral and intraoral disinfection, respectively. Lidocaine plus epinephrine (Persocaine-E®, Darou Pakhsh Pharmaceutical Mfg. Co., Tehran, Iran) was used for local anesthesia. Gingival recession defects were treated according to the Langer and Langer technique [7]. A partial-thickness flap was elevated with two vertical incisions wider than the recession area by the length or half-length of a tooth mesiodistally. The coronal margin of the flap was prepared by a sulcular horizontal incision.
Interdental papilla remained untouched. The flap was extended to the mucobuccal fold without causing any perforation. Root surfaces were curetted to eliminate irregularities and dental plaque. A proper size connective tissue graft with 2 mm thickness was harvested from the palate using the trap-door technique [14]. The area was sutured with non-resorbable stitches (Braided Silk 4-0, SUPASIL, SUPA Medical Devices Co., Tehran, Iran). Er,Cr:YSGG laser (Waterlase; Biolase. Technologies, San Clemente, CA, USA) was used for root surface conditioning in the case group. The laser optic fiber was positioned perpendicular to the surface at a distance of 1-2 mm. The laser was irradiated at 2780 nm wavelength, 20 Hz repetition rate, 0.75 W power, H mode [28] with 60% water and 40% air, using a Gold handpiece with MZ6 tip (600 µm in diameter and 6 mm in length) in spiral motion (vertical, horizontal, and oblique directions) and defocused mode. Eyeglasses with a suitable optical density were worn. The graft was trimmed if required and was then fixed at the recipient site using resorbable stitches (Polyglycolate coated 4-0, SUPABON, SUPA Medical Devices Co., Tehran, Iran). For better blood supply, the flap covered a large part of the graft. Eugenol-free periodontal dressing (Coe-Pak, GC America, Alsip, IL, USA) was applied on the surgical site and was repeated after one week. At the end of the second week, the stitches were removed. The root coverage treatments in each patient were performed with an interval of 6 weeks between the first and the second surgeries. teeth at the surgical site for 14 days. Also, 0.2% chlorhexidine mouthwash was prescribed twice a day, each time for one minute. The sutures were then removed, chlorhexidine was prescribed for two more weeks, and tooth brushing with a soft toothbrush was recommended twice a day. Dental prophylaxis was performed two weeks after suture removal and then monthly until the end of the study period.To ensure the absence of bias, all surgical treatments were done by a single surgeon, whereas the clinical measurements were made by another examiner. Figure 1 shows the stages of the treatment in a patient.

Assessment of root coverage:
The percentage of root coverage was calculated using the following formula: Root Coverage (RC) = (Preoperative RD -Postoperative RD) / Preoperative RD × 100 Data analysis: Data were analyzed by SPSS version 24 software program (SPSS Inc., Chicago, IL, USA). Descriptive data were reported. Since data were not normally distributed according to Kolmogorov-Smirnov test, non-parametric tests were used for data analysis. Intragroup comparisons of the variables were made using Friedman test.   These improvements were significant at 2 and 6 months compared to the baseline (P=0.001) and also at the time interval between 2 and 6 months (P=0.007).
The same changes were recorded in the control group. A significant reduction occurred in RD from 3.20±0.77 mm at the baseline to 1.22±0.93 mm at 2 months and 0.96±0.73 mm at 6 months postoperatively (P=0.001). This reduction during the time interval between 2 and 6 months was not significant (P=0.083), but the reduction at 2 and 6 months compared to the baseline was statistically significant (P=0.001). RW decreased from 2.47±0.74 mm at the baseline to 1.30±1.00 mm at 2 and 6 months (P<0.001); this reduction was statistically significant compared to the baseline (P=0.001). A significant reduction occurred in CAL from 4.67±1.11 mm at the baseline to 2.40±1.68 mm at 2 months and 1.80±1.32 mm at 6 months postoperatively (P<0.001). The reduction at 2 and 6 months was significant compared to the baseline (P=0.001), but the change during the time interval between 2 and 6 months was not statistically significant (P=0.014). PD did not experience any significant change at the mentioned time points in any group (P>0.05). No significant difference was found in root coverage between the case and control groups postoperatively (P>0.05, Table 2). Table 3 shows the frequency of complete root coverage achieved postoperatively in the two groups.

DISCUSSION
The current study showed that the use of Er,Cr:YSGG laser for root surface conditioning had no significant effect on the outcome of the treatment of gingival recession with SCTG. The mean CAL, RD, and RW in both groups significantly decreased during the study period. The mean root coverage in the case and control groups at 2 months postoperatively was 81% and 74%, respectively. These values were 87% and 80% at 6 months, respectively. Complete root coverage in both groups had a frequency of 60% at 2 months. This value in the case group increased to 67% at 6 months but remained unchanged in the control group. These findings are comparable to those of previous studies reporting a range of 64.7% to 97.3% for the mean root coverage and 18.1% to 96.1% for complete root coverage [16,21,29]. The commonly used modalities for the treatment of gingival recession during the 1960s and 1970s included free gingival graft [6] and pedicle grafts [8-10]. SCTG was used for this purpose in the early 1980s [7]. Several studies have reported the high success rate and high predictability of this approach [13][14][15]. Thus, SCTG was used for the treatment of gingival recession in this study. The final goal of the treatment of gingival recession is to achieve complete root coverage to improve esthetics and eliminate tooth hypersensitivity [16,21,29]. Several conditioners have been used for this purpose, but controversy exists regarding their efficacy for the improvement of clinical parameters.   [35,36]. Clinical studies have reported the optimal efficacy of erbium laser for the treatment of periodontal pockets via surgical and non-surgical techniques [37,38] and also for root conditioning [39,40]. Changes caused by the thermomechanical effects of Er:YAG laser on the root surface include a change in the microstructure as well as thermal alterations [34,[41][42][43]. The changes occurred in surface microstructure are considered advantageous for the primary attachment of cells and tissues in the clinical setting and result in the better formation of fibrin and blood clots [41][42][43]. Due to high absorption in water, erbium lasers have a high power for ablation of dental hard tissues [34,35] without causing significant thermal complications such as carbonization, melting, or crack formation in the root structure, which are often seen following the use of CO2 and Nd:YAG lasers [34,44]. Considering the biocompatibility of the surfaces lased with Er:YAG laser, several studies have shown the better attachment and faster proliferation of fibroblasts on these surfaces compared to mechanically debrided surfaces [17,45]. The Er,Cr:YSGG laser parameters used in this study included 2780 nm wavelength, 0.75 W power, H mode, and 20 Hz repetition rate, according to the recommendations of a previous study, to preserve the biocompatibility of lased root surfaces [28]. In contrast, some authors reported that root surfaces lased with Er:YAG laser showed significant micron-scale irregularities in vitro [41,43]. Fujii et al [41] demonstrated that lased root surfaces had a specific microstructure along with denatured collagen fibers. Regarding other lasers, Trylovich et al [46] reported that the application of Nd:YAG laser changed the biocompatibility of root surfaces, making them unsuitable for the attachment of fibroblasts. Fayad et al [44] reported the complete absence of fibroblast attachment to root surfaces following the use of CO2 laser. Some recent studies indicated that the application of Er:YAG laser significantly improves a number of clinical parameters [17,37,38]. Dilsiz et al [3] discussed that the application of Er:YAG laser for root biomodification does not improve the results of SCTG. Bouchard et al [47] and Caffesse et al [18] reported that root surface conditioning with citric acid has no effect on the clinical results of SCTG. Our findings were in agreement with their results. Further clinical studies are required to confirm the results of this study in larger study populations with longer follow-up periods.

CONCLUSION
According to the results of this study, root surface conditioning by Er,Cr:YSGG laser improved the mean root coverage and the percentage of complete root coverage. However, these changes were not statistically significant.